Herbicides

Herbicides, also known as weed killers, are chemical substances used to control unwanted plants. They are an important tool in farming, gardening, and landscape turf management. Herbicides work by targeting specific physiological processes that are essential for plant growth and development, which are often distinct from those in animals, making them selective to plants.

Types of Herbicides

Herbicides can be classified based on their mechanism of action, timing of application, selectivity, and persistence.

Selective vs. Non-selective

• Selective herbicides control specific weed species, while leaving the desired crop relatively unharmed.
• Non-selective herbicides (or broad-spectrum herbicides) kill all plant material with which they come into contact.

Contact vs. Systemic

• Contact herbicides kill only the plant parts they touch, and are effective for annual weeds.
• Systemic herbicides are absorbed and move within the plant to reach areas such as roots, making them effective against perennial weeds.

Pre-emergent vs. Post-emergent

• Pre-emergent herbicides are applied before the weeds germinate.
• Post-emergent herbicides are used after the weeds have emerged.

Mechanism of Action

Herbicides disrupt various plant processes including photosynthesis, amino acid synthesis, and enzyme activity. Some common mechanisms include:

• Inhibition of Photosynthesis (e.g., atrazine)
• Inhibition of amino acid synthesis (e.g., glyphosate)
• Disruption of cell division (e.g., pendimethalin)

Usage

Herbicides are used in various settings:

• Agriculture: to increase crop yield by reducing weed competition.
• Horticulture and landscaping: to maintain weed-free lawns and ornamental plants.
• Forestry: to manage undergrowth in forested areas.

Environmental Impact

The use of herbicides raises concerns regarding environmental impact and human health. Issues include:

• Pollution of water bodies through runoff.
• Development of herbicide-resistant weed species.
• Potential toxicity to non-target species, including humans.

Regulation and Management

Herbicide use is regulated by governmental bodies to ensure that they are used safely and effectively. Farmers and land managers are encouraged to use integrated weed management (IWM) strategies to minimize reliance on chemical weed controls.

See Also

• Pesticide
• Insecticide
• Fungicide